The present invention relates to the field of contour gages, and more particularly to a method for measuring the contour of a machined part on a gage that accurately and automatically measures internal and external dimensions of hemispherical parts, both convex and concave.
In the art of measuring curved surfaces, U.S. Pat. No. 3,911,257 of Whitehouse et al is known. This patent is directed to an instrument to measure surface finish on cylindrical parts. The measurement is exclusively two dimensional. Only a very small slice of the overall shape and dimension of a part is carried out with each measurement. However, it would be desirable to be able to measure three-dimensional surfaces.
In accordance with the Whitehouse et al patent, only outside diameters or outside contours can be measured. The measurement plane is related to the location of the stylus, and the measurement is represented as a signal which relates to the variation in out of roundness of the workpiece being measured and the roughness of the surface of the workpiece. However, it would be desirable to be able to measure contours of interior surfaces as well as outside contours.
The measurement system described in the Whitehouse et al patent is not suitable for use on a machine tool whereby a machined part is measured while it is still in the machine tool fixture. To use the Whitehouse et al system, each machined part must be removed from the production equipment and then measured with the system. It would be desirable, however, to have a contour gage and corresponding method of use for measuring a machined part while it is still associated with the machining equipment that produced the part.
For the Whitehouse et al device to carry out its measurements, the device needs to perform one complete revolution to permit an eccentricity term to be computed. The computation of the eccentricity term is derived from the signals provided by a sensor applied to the part being measured. Radius suppression and signal magnifications are necessary to actually display a measured shape of an outside contour of a part.
Furthermore, with the patent of Whitehouse et al, the disclosed device cannot measure the height of a part or the pole height radius of a hemispherical part. With certain types of parts, only the eccentricity of a part at a given distance around the equator of the part could be measured. It would be desirable, therefore, to have a contour gage and corresponding method of use for making more complete measurements with machined parts.
In general, the prior art is very limited in its disclosure of on-machine gages that permit contour measurements of machined parts while they are still on the machining equipment. Industry generally separates the task of production from the task of inspection such that these risks are performed by two different departments in two different environments.
Among the limited prior art gaging devices that are used to measure the surfaces of machined parts while still on the machine tool, some gaging devices employ touch probes that are used in place of the cutting tool. Such touch probes use the slides of the machine tool and are limited to a point-to-point contact probing mode of operation. Consequently, such touch probe gages cannot perform any scanning action on the machined contour. It would be desirable, however, to have a contour gage and corresponding method of use that did not use the slides of the machine tool and that performed a scanning action on the machined contour.
Other prior art gaging devices are known as array gages. With array gages, multiple individual LVDT probes are used to collect data relative to the machine tool. These array gages are dedicated to one type of part and are not flexible for use with a variety of part types. Furthermore, with array gages, a spiral probing pass is not possible since the spacing between LVDT probes determines the area to be inspected. Only a number of diameters away from the equator of the part are evaluated giving very little detail about the overall contour of the part being measured.
In the prior art, rotary encoders are either mounted right on an axis of a turning spindle, or the encoder is directly coupled to the shaft of a motor which controls a gage. In a rotary encoder mounted directly on a spindle, when the spindle undergoes one revolution, the encoder undergoes one revolution. This arrangement prevents accurate resolution of rotary motion of the spindle. More specifically, in 360 rotary degrees there are 21,600 rotary minutes (360.times.60) and 1,296,000 rotary arc seconds (21,600.times.60). If it is desired for a rotary encoder to have a resolution of 1 arc second, then the encoder would have to provide 1,296,000 individual increments for a 360 degree revolution. Such a fine resolution is not available in present encoders. It would be desirable, however, to obtain a rotary encoder and corresponding method of use that is capable of providing a resolution of 1 arc second of rotation.
In an encoder which is coupled to the shaft of a motor, the encoder will not detect any slippage that may result between the drive pulley on the motor and a rotary spindle. It would be desirable to have an encoder and corresponding method of use which would not be susceptible to error resulting from slippage between a drive motor and a rotary spindle.
There are known gages which utilize two linear Cartesian motions (e.g. an X and a Y) to gage circular surfaces with a probe. With such a Cartesian driven probe, the angle between the probe and the surface being gaged is constantly changing and is other than normal to the surface, except when the angle between the X and Y motions is 45 degrees. With the Cartesian driven probe, there may be heavy side loads exerted on the probe by the surface that is being gaged. Side loads being exerted on the probe can be the cause of erroneous data with respect to the gaged surface. It would be desirable to have a probe system which constantly maintains the probe substantially normal or perpendicular to the surface being gaged thereby avoiding side loads being exerted on the probe.
Accordingly, it is a primary object of the present invention to provide a precision gage and method for its use, to provide for contour measurements of three-dimensional surfaces.
Another object of the invention is to provide a precision gage and method for its use, to measure the contours of interior surfaces as well as the contours of exterior surfaces, especially of hemispherical parts.
Another object is to provide a contour gage that can be used to measure the contour of a part while it is still associated with the machining equipment that produced the part.
An additional object of the invention is to provide a precision contour gage that does not use the slides of a machine tool and that performs a scanning action on the machined contour.
A further object of the invention is to provide a rotary encoder, and method for its use, that is capable of providing a resolution of 1 arc second of rotation.
Yet another object is to provide an encoder and method for its use, that is not susceptible to error resulting from slippage between a drive motor and a rotary spindle.
Still another object of the invention is to provide a probe system which constantly maintains the probe substantially normal to the surface being gaged thereby avoiding side loads being exerted by the surface onto the probe.
Additional objects, advantages, and novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.